This invention is directed to a process and apparatus for filling tires with nitrogen gas (N2). More particularly, this invention is directed to a process and apparatus for efficiently filling large size vehicle tires such as truck and bus tires with nitrogen gas.
When compressed air is introduced into a tire, via a compressor open to the ambient atmosphere, water vapor and other impurities are introduced into the tire. With moisture and other impurities present, the air volume in the tire, fluctuates fairly widely with temperature, particularly due to moisture changing from liquid to vapor form and vis-versa as temperatures in the tire change. As a rule of thumb, tires inflated with compressed ambient air will change about 1psi for every 10 degree Fahrenheit change in temperature. Thus, a tire inflated at 60 degrees Fahrenheit will be substantially under inflated at 20 degrees due to the combined effects of temperature in reducing gas pressure and moisture condensing out of the air within the tire. Conversely, as temperatures increase to 90 degrees Fahrenheit, the tire will be substantially overinflated due to the water being vaporized and the attendant increase in air pressure due to temperature. Those under or over inflation conditions can adversely affect rolling friction of tires on pavement, thus decreasing gas mileage. Tire wear is also increased when the tires are not inflated to the manufacturer""s recommendations. Water vapor within tires may also induce rust within steel belted radials, which further reduces tire life.
In order to reduce or eliminate these problems, race cars, earthmoving and mining equipment, and commercial and military aircraft often utilize tires inflated with compressed nitrogen. Nitrogen is an ideal gas for such a purpose since it is chemically inert, non-combustible, non-flammable and non-corrosive, and when dry, is relatively stable in volume through a wide range of temperatures. For example, the specific volume of a quantity of dry nitrogen gas at 1 atmosphere of pressure varies less than 13% in a range of xe2x88x9210 degrees F. to +116 degrees F. Thus, the use of nitrogen to inflate a pneumatic tire offers a reduction in fluctuations of internal tire pressure due to temperature variations over those which occur when moisture laden compressed ambient air is used.
In view of the above, it is believed that filling a tire with N2 gas may help the degradation of rubber and the like. Known systems of providing N2 gas for tire inflation include a method wherein N2 gas is separated and purified from air using industrial activated carbon, a method of using a gas separation membrane wherein O2 and N2 are separated from air by utilizing different permeation rates, and by simply using an N2 filled canister.
While these several known systems for providing N2 gas for tire inflation provide benefits, each also demonstrates certain drawbacks. For example, N2 gas canister storage requires significant physical space to maintain a sufficient supply. Furthermore, transporting canisters to a filling station is both inconvenient and costly. The carbon or membrane separation apparatus can be problematic because of low N2 separation rates, resulting in long filling times. In a commercial operation, extended filling times can render the process undesirable to consumers. This problem can be particularly severe when the system is used with large tire vehicles such as bus or truck. Accordingly, an improved system/process for N2 tire inflation would be desirable.
According to one embodiment of the invention, a method of inflating a tire is provided. The method involves the use of an apparatus including a membrane and a storage tank and includes the steps of separating N2 gas from air using the membrane and providing the N2 gas to a storage tank having capacity for storing at least 40 cubic feet of N2 gas at 18xc2x0 centigrade. Preferably, the storage tank is separately transportable from the membrane, i.e., they are independent units. Thereafter, N2 gas is provided from the storage tank to a hose, the hose including a pressure gauge, a stop valve, and a fitting suited for mating with a tire inflation valve stem. The fitting is secured to the tire inflation valve stem and the stop valve opened to initiate introduction of the N2 gas into the tire. Preferably, the storage tank will include the capacity for between 50 and 600 cubic feet of N2 gas at 18xc2x0 centigrade. Preferably, the storage tank is able to accommodate said N2 gas up to at least 100 psig, more preferably at least 200 psig. Preferably, the N2 gas will be provided to the tire at a pressure of at least 110 psig.
According to another embodiment of the invention, an apparatus for inflating a tire with N2 gas is provided. The apparatus includes a mechanism supplying compressed air to a membrane which separates N2 and O2 gas. The apparatus further includes a fluid path providing the N2 gas to a storage tank having capacity for storing at least 40 cubic feet of N2 gas at 18xc2x0 centigrade. A hose, including a pressure gauge, a stop valve, and a fitting suited for mating with a tire inflation valve stem is provided in fluid communication with the storage tank.